How does food get genetically modified?

Genetically Modified Rice Plants
Credit: BASF Flickr

As the season of eating way too much continues through the holidays, many of us will be enjoying recipes and traditions that are centuries old. But the great majority of these annual feasts — like most food Americans eat every day — is decidedly from the 21st century, and the product of biotechnology.

Since their introduction 18 years ago, genetically modified organisms (GMOs) have largely taken over our farm fields. To give one example, in 2013, 93 percent of the soybeans grown on American soil were genetically altered to resist herbicides. But what does that really mean? How does genetic engineering work? At a basic level, it means altering the DNA of crop plants to endow them with new and non-native traits, which may help them grow bigger, or confer resistance to herbicides or insects. Humans have been changing genetic expression in food with methods like selective breeding for thousands of years — just not this way. Here’s how it’s done now.

Getting New Genes

Before you modify a plant’s DNA, you need to know what, exactly, to change. Do you want the plant to withstand a weed killer, like Roundup? Or do you want it to survive insects that attack its roots or fruit? Maybe you want it to contain more healthy fats like oleic acid, or beta carotene to produce vitamin A. First, you’ll need to hunt for the genes that produce these traits in other plants (or animals), and you'll have to figure out what makes them effective.

Herbicide tolerance is just one example. The Monsanto Company makes the weedkiller Roundup, which includes glyphosate as its main ingredient, which interrupts plants' ability to synthesize amino acids. If the crop plants that we like to eat could withstand glyphosate, farmers could then spray their fields to control weeds but spare their crops, making this resistance a valuable trait. But traditional methods of breeding wouldn't be able to introduce this trait — it comes from a species of bacteria. No amount of Barry White would allow Monsanto to crossbreed bacteria and soybeans, so instead, the company's scientists introduced glyphosate tolerance directly, through the plants' DNA.

 Roundup at the Ready

"The first thing you need to do is understand the problem at the biochemical level," says Bruce Chassy, professor emeritus of food science and nutritional sciences at the University of Illinois at Urbana-Champaign. "If you can identify one or more strategies that involve using genetics to change the plant, you start looking if there are genes out there that have been characterized to do what you want to do."

Once you've got the genes, you’ll want to coax plant cells back to their very beginnings — the plant equivalent of the zygote, a single undifferentiated cell. That way, every other cell that divides during development will have the same already-altered DNA. You could do this using the plant embryo, which lives inside every seed, or you could culture tissues in a lab.

Genetic Transfer

Then you would introduce your new gene, using one of two main methods: a Trojan-horse strategy mediated by bacteria, or a shotgun approach. The latter, first developed in 1987, is less common today. It literally shoots a gene gun, a technique called "biolistic particle delivery," to blast genetic material into plant cells.

"The idea is you would deliver micron-sized particles into the nucleus, or very close to the nucleus, and the DNA migrates and is integrated into the cell," says Nigel Taylor, senior research scientist and principal investigator at the Donald Danforth Plant Science Center in St. Louis. The cells’ own DNA repair mechanisms then incorporate the genetic material as their own.

This is somewhat inelegant, because only a small percentage of the thousands or millions of cells in this process would incorporate the new DNA in the correct sequence. It’s simpler to use a strategy from Agrobacterium tumefaciens, which evolved to glom onto plant tissues and inject its own genes. 

Methods of Gene Transfer

This bacteria works by implanting plasmid DNA, a type of DNA molecule that’s separate from the bacteria’s own chromosomes, into the roots of stressed-out or wounded plants. In this photo, A. tumefaciens is attaching itself to a tasty carrot cell. Plasmid DNA encodes enzymes that make the plant produce sugars and amino acids, which the bacteria takes advantage of, Chassy says. Biotechnologists can harness this capability by replacing the bacteria plasmid with something else. It could be a DNA sequence for conferring resistance to the chemicals in Roundup, for instance. 

"Now when the bacterium infects cells, it inserts the gene that you want in there, usually in a single copy in a single place," Chassy says. 

Next, you can figure out whether it worked as planned, and whether the plant will do what you want.

What About Hybridization And Traditional Breeding?

The transformed embryonic plant cell goes into a cell culture, where it’s fed a broth that encourages it to differentiate. The result is a small shoot, a "plantlet," that you can grow. You might use genetic markers, polymerase chain reactions, or other molecular biology techniques to study its DNA and make sure it has the right genes in the right spots on the genome, Taylor says.

"You have to find the right culture, the right nutrient conditions, the right temperature; that’s kind of the art of the science," Taylor continues. "Once you’ve identified those guys, you could put them into a greenhouse and see how they perform. You could analyze them to see if they are making the product you want."

Assuming all has gone to plan so far, the next step would be to cross-breed the plants that have the genes and traits you’re looking for. In this effort, modern biotechnology works the same way plant breeding has worked for millennia, Chassy and Taylor say. You find a plant with a characteristic you like, and you cross it with another plant whose characteristics you want to pass down.

Golden Rice

In the days before recombinant DNA technology, breeders used radiation, heat, chemicals and other processes to mutate plants, Chassy adds. "It’s simply a powerful tool," he says of genetic engineering. "In their quivers, breeders have a bunch of other arrows they also use."

As Taylor points out, it’s not as though biotechnology replaces or supplants breeding. "All of those what some people call 'traditional techniques,' they’re still used. Now they’re enhanced," he says. "What this does is bring new traits into the breeding program that were not available, or very difficult to fix, before biotechnology existed."

Is It Safe?

After being engineered and cross-bred, the genetically modified plant progeny are grown in fields across at least three continents, and are subject to scrutiny from a handful of regulatory agencies around the world. Only after it passes those trials will the seeds of these plants be considered fit for humans — and our livestock — to eat. 

Based on decades of research, the short answer, from a vast, international scientific consensus to the question above, is "yes."

This is from the American Association for the Advancement of Science, put out in a statement last fall: "The World Health Organization, the American Medical Association, the U.S. National Academy of Sciences, the British Royal Society, and every other respected organization that has examined the evidence has come to the same conclusion," AAAS notes. "Consuming foods containing ingredients derived from GM crops is no riskier than consuming the same foods containing ingredients from crop plants modified by conventional plant improvement techniques. …Civilization rests on people’s ability to modify plants to make them more suitable as food, feed and fiber plants and all of these modifications are genetic."

Opponents of genetically modified crops, including Greenpeace, the Organic Consumers Association, the Union of Concerned Scientists, food writers, and others, argue that the risks of these foods haven’t been fully recognized. They also question whether regulators can objectively study the question, when much of the published research has been funded by seed producers like Monsanto and DuPont Pioneer. Some groups have organized efforts to require genetically modified products to carry additional labels, putting the question to voters in Washington and California. Both these efforts failed, though opponents say they will keep fighting.

Anti-GMO Protesters

Scientists including those from UCI argue that genetic engineering is not the solution to the world's food problems. Others note that herbicide-tolerant plants encourage farmers to spray weedkiller with abandon, and this has led to herbicide-tolerant "superweeds." It's a serious enough problem that Monsanto has paid farmers to spray herbicides from its competitors, too, to give fields a break.

Food scientists like Chassy, whose research included recombinant DNA techniques for manipulating food-related microbes, believe GM crops are over-regulated and wrongly hyped.

"In the midst of all the clamor, it is often overlooked that the effect of all breeding is to change the DNA in some way," Chassy says. "Every new variety of every new crop is a mutant, or a genetically modified, seed. If unintended effects are possible, they’re equally possible from other methods of breeding, too."

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